Subsea stab plates contain an array of equipment, typically self-sealing hydraulic couplings and/or electrical connections. There is typically a fixed stab plate which is attached to a sub-sea structure to which hydraulic or electrical lines are run to an array of fixed half-couplings on this stab plate. The free stab plate has a corresponding array of the free halves of the electrical and hydraulic couplings to which hydraulic tubes or electric cables connected to surface equipment are attached. A so-called umbilical connection, often many kilometers long, takes the supply lines from the surface equipment to the free stab plate.
Initially the free stab plate would be at the surface awaiting deployment. The free stab plate would then be transported, preferably by means of a remote operated subsea vehicle (ROV), to the subsea structure.
The invention relates to the means whereby two members, and particularly a ‘free’ plate and a ‘fixed’ plate, are oriented to accept each other, captured, brought together and clamped. An important requirement of the device is that it shall be possible to unclamp and remove the free plate.
It is known to provide on the fixed plate a central thread engageable with a rotatable nut loosely clamped to the centre of the free plate. Such a nut has to be accessible even though it be surrounded by stab couplings and hose lines, and for this purpose it is customary to arrange the hose lines to extend sideways from the free plate and to extend the nut to be clear of the hoses and/or supply lines.
A securing device, which comprises a drive shaft longitudinally reciprocable forwards and backwards along its axis and having at one end a head adapted to pass forwards through a key aperture in a wall member when the drive shaft is in at least a first angular position, the head being adapted to engage the wall member when the drive shaft is in a second angular position and is moved rearwards, is known from the document OTC 6720, Proceedings of the 23rd Offshore Technology Conference, Houston, Tex., May 1991 pages 209-220.
The present invention relates to a improved device which has a more general utility but in the subsea context facilitates clamping and also facilitates removal of the free plate even in the event of seizure of parts or fouling of the device by marine growth, so that for example the free plate may be removed and taken back to the surface for repair while the fixed plate remains on the subsea structure in an immediately reusable condition.